1. Field of the Invention
The present invention relates to an active matrix LCD (liquid crystal displaying device).
2. Discussion of the Background
In recent years, the LCD is improved for higher image quality and larger image field as a display instead of a CRT. Thus, a new material is used, and the manufacturing process and the configuration in using it are considered.
One example of the aforementioned conventional LCD will be described hereinafter with reference to the accompanying drawings.
FIG. 10 is a sectional view of the essential portions of a TFT array substrate of the LCD to be used in the conventional LCD. Referring to FIG. 10, reference numeral 201 is a TFT portion, reference numeral 202 is a gate source intersecting portion, reference numeral 203 is an auxiliary capacitance portion, reference numeral 17 is a convertor, reference numeral 27 is a pixel electrode, reference numeral 60 is a first conductor, reference numeral 61 is a second conductor, and reference numeral 54 is a third conductor.
The conventional LCD is composed of a TFT array substrate, an opposite substrate arranged opposite to the TFT array substrate, and a liquid crystal to be interposed by both the substrates, with the periphery of both the substrates being bonded with a sealing agent. On the TFT array substrate are provided a plurality of mutually parallel gate wirings and a plurality of mutually parallel source wirings to be crossed to the respective gate wirings through the gate insulating film to be rovided on the gate wirings, with the pixels being regions to be defined by the gate wirings and the source wirings. On each pixel are provided in array-like shape pixel electrodes and TFT (thin film transistors). An alignment layer is provided, covering the gate wirings, the source wirings, the pixel electrodes and the TFT (in the conventional example, a channel etch type). On the opposite substrate are provided a color filter, a black matrix, and an alignment layer corresponding to the pixel. The liquid crystal uses the known liquid crystal material.
In order to drive such a liquid crystal, a drive circuit is provided around the LCD. Behind the LCD is sometimes provided a back light.
In order to connect the pixel electrode provided on the TFT array substrate, and the TFT and the drive circuit, various conductors and contact holes are provided on the TFT array substrate to connect the gate wiring and the source wiring.
FIGS. 11-13 show a disclosure from a related Japanese Application Serial No. 124601/1998, the Applicant of which is the same as that of the instant application, which had not been published at the time of the Japanese priority document on which the presgfit document is based was published.
FIG. 11 is a plan view showing the arrangement of the wirings, terminals and so on provided on the TFT array substrate. Referring to FIG. 11, reference numeral 12 is a gate wiring, reference numeral 13 is a source wiring, reference numeral 72 is a gate terminal, reference numeral 73 is a source terminal, reference numeral 60 is a first conductor, reference numeral 61 is a second conductor, reference numeral 54 is a third conductor, and reference numeral 17 is a convertor. The right side and the under side of one dot chain line L are displaying regions.
As shown in FIG. 11, the gate wiring 12 and the gate terminal 72 are connected with the first conductor 60. The source wiring 13 and the source terminal 73 are connected by the first conductor 60 and the second conductor 61 through the third conductor 54. Such connecting method is used because the material for connecting with the terminal is made of a material superior in corrosion resistance or a material low in wiring resistivity. In an example shown in the diagram, the gate wiring is composed of the first conductive material, and the source wiring is composed of the second conductive material, with the material of the gate wiring being superior in corrosion resistance. In this case, on the source wiring side is provided a convertor 17 to which the first conductor and the second conductor are connected through the third conductor.
FIG. 12 is a sectional view showing the connection between such a conductor and a contact hole. FIG. 13 is a sectional view showing the example where the connection is provided in contact with the liquid crystal.
In FIG. 12 and FIG. 13, reference numeral 21 is an insulating substrate (hereinafter referred to as a substrate) using the insulating material such as glass, reference numeral 60 is a first conductor formed on the substrate 21 using the conductor such as Cr, reference numeral 61 is a second conductor formed on the substrate 21 using the conductor such as Cr, reference numeral 23 is a first insulating film formed on silicon nitride or the like, reference numeral 102 is a second insulating film formed on the silicon nitride or the like, reference numeral 103c is a contact hole formed on the first conductor 60, reference numeral 103d is a contact hole formed on the second conductor 61, reference numeral 54 is a third conductor using a conductor such as Cr for connecting the first conductor 60 and the second conductor 61 through the contact hole 103c and the contact hole 103d, reference numeral 17 is a convertor for connecting the first conductor 60 with the second conductor 61 with the material being changed with the third conductor 54, reference numeral 50 is a liquid crystal, reference numeral 51 is a sealing agent, and reference numeral 53 is an opposite substrate.
In the convertor 17 shown in FIG. 12, there is no passivation film made of a material such as silicon nitride on the third conductor 54. Thus, in the LCD having the convertor 17, such problems as described hereinabove are caused.
The problems will be described with reference to FIG. 13. The first conductor 60 is a wiring, formed with the gate wiring material, to be connected with the external terminal. The second conductor 61 is a wiring, formed with a source wiring material, to be connected with the external terminal, with the third conductor 54 functioning to connect the first conductor with the second conductor. The reasons to be adopted in such a configuration are provided because (1) the wiring to be connected with the external terminal, as described, is required to be formed in the gate wiring material, when the source wiring material tends to corrode more than the gate wiring material, and (2) a process for forming a contact hole for directly connecting the external terminal formed with the source wiring and the gate wiring material is omitted. The third conductor 54 is formed of the same material as that of the pixel electrode for applying the voltage upon the liquid crystal in the display region and an insulating film is not provided on the pixel electrode to reduce the loss of the voltage to be applied upon the liquid crystal. To cover the third conductor with the insulating film, a new process is required and the cost increases. The third conductor is provided as the uppermost layer and is exposed. In the LCD in which the convertor 17 is provided in such a manner as to directly contact with the liquid crystal 50 as shown in FIG. 13, the third conductor 54 of the convertor 17 is in contact with the liquid crystal 50 and a signal to be applied upon the first conductor 60 or the second conductor 61 is applied upon the liquid crystal 50 with the third conductor 54 as an electrode. Thus, the liquid crystal near the third conductor 54 is deteriorated, resulting in inferior display and the reduced reliability.
When the gate wiring material uses a material which tends to corrode more than the source wiring material, the gate wiring is required to be connected with the external terminal through the wiring made of a source wiring material. In this case, the wiring material is required to conduct, through the third conductor, so that the gate wiring may be connected with the wiring, connected to the external terminal formed made of the source wiring material. Thus, due to direct contact between the third conductor 54 hand the liquid crystal as in the configuration shown in FIG. 13, the liquid crystal near the third conductor 54 is deteriorated, thus resulting in the inferior display and reducing the reliability.
Since the third conductor 54 of the conductor 17 comes in contact with the liquid crystal as described above in the conventional LCD, the reliability is reduced. An object of the present invention is to provide an LCD element and an LCD higher in reliability, by solving the aforementioned problems.